This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to improving data transfer rate performance by writing data to a magnetic medium using discrete pulsed write currents.
Disc drives are used as primary data storage devices in modern computer systems and networks. A typical disc drive comprises one or more rigid magnetic storage discs which are journaled about a spindle motor for rotation at a constant high speed. An array of read/write transducing heads are provided to transfer data between tracks of the discs and a host computer in which the disc drive is mounted. The heads are mounted to a rotary actuator assembly and are controllably positioned adjacent the tracks by a closed loop servo system.
Each of the disc surfaces is provided with a magnetizable media coating to retain the data as a series of magnetic domains of selected orientation which are impressed by a write element of the corresponding head and subsequently detected by a read element of the head. Although a variety of head constructions have been utilized historically, magneto-resistive (MR) heads are typically used in disc drives of the present generation. An MR head uses a thin-film inductive coil arranged about a ferromagnetic core with a write gap so that, as write currents are passed through the coil, magnetic flux lines fringing across the write gap extend into the adjacent media to establish magnetization vectors, or intervals, in directions along the track. Magnetic flux transitions are established at boundaries between adjacent intervals of opposite orientation, and these flux transitions (each indicative of a logical one) are detected by an MR read element which has a characteristic electrical resistance that changes in the presence of a magnetic field. Thus, by passing a small biasing current through the MR read element, the flux transitions can be transduced in relation to the voltage across the MR read element.
To write a computer file to disc, a disc drive receives the file from the host computer in the form of input data which are buffered by an interface circuit. A write channel encodes and serializes the data to generate a data stream that can be represented as a square-wave type signal with varying interval (symbol) lengths between successively occurring rising and falling edges. The placement of the rising and falling edges correspond to the logical ones in the data sequence.
A preamplifier/driver circuit (preamp) uses the data stream to generate write currents which are applied to the head to write the encoded data to the selected disc surface. Typically, disc drives use a continuous write current that toggles from a maximum current value of a first polarity (such as +50 milliamps, mA) to a corresponding maximum current value of a second, opposite polarity (such as xe2x88x9250 mA), with the periodic changes in current direction inducing the aforementioned flux transitions on the media. Such methodology is discussed, for example, in U.S. Pat. No. 5,159,501 issued Oct. 27, 1992 to Genheimer.
While constant current recording has been found useful, it becomes increasingly difficult to write the data using a continuous current at higher transfer rates such as greater than one gigabit (Gb) per second (1xc3x97109 bits/sec), due to various factors including stray inductance and capacitance along the conductive paths between the heads and the preamp, the slew rate in the positive and negative transitions, and the power dissipated by the preamp.
As an alternative to a continuous write current, impulse magnetic recording has been proposed in the prior art as discussed by U.S. Pat. No. 4,562,491 issued Dec. 31, 1985 to Kawabata et al. and U.S. Pat. No. 4,965,873 issued Oct. 23, 1990 to White. Kawabata et al. proposes writing data to a magnetic medium by converting each continuous current pulse into a series of very short duration, discrete pulses for each interval. By time shifting the pulses supplied to a number of different heads, data can be written to multiple heads at the same time using a single power supply with a current output capacity sufficient for only one head. White also proposes writing data using a series of positive and negative transition pulses of very short duration. White uses higher amplitude transition pulses to write flux transitions and uses additional, lower amplitude sustaining pulses of the same polarity to sustain the recorded magnetic field for longer intervals between successive transition pulses. It will be noted that both Kawabata et al. and White are directed to relatively lower data transfer rates and use multiple current pulses to write the magnetization vectors.
While operable, there remains a continued need for improvements in the art to enhance magnetic write performance at ever increasing data transfer rates. It is to this end that the present invention is directed.
The present invention provides an apparatus and method for improving disc drive data transfer rate performance.
In accordance with preferred embodiments, a disc drive comprises a rotatable disc to which data are stored as a sequence of magnetization vectors having alternating magnetic orientation and associated lengths that range from a minimum symbol length (such as 1T) to a maximum symbol length (such as 6T).
A write element is provided having a leading edge and a trailing edge to form a write gap therebetween, the write gap generating a write gap recording field having a length substantially greater than the minimum symbol length. A first current pulse is applied to the write element to magnetically orient a first area of the magnetic medium in a first direction. A second current pulse is subsequently applied to the write element to magnetically orient a second area of the magnetic medium in a second direction opposite the first direction. The first and second current pulses have opposing polarities and respective short durations with respect to a period of time required for a point on the magnetic medium to traverse the write gap.
The second current pulse is applied while a portion of the first area remains between the leading edge and the trailing edge of the write element so that the portion of the first area is magnetically reoriented by the second current pulse. The remaining portion of the first area disposed beyond the trailing edge of the write element comprises a magnetization vector of desired symbol length.
In one preferred embodiment, the length of the write gap recording field exceeds the maximum symbol length. In such case, the application of each current pulse is sufficient to magnetize the medium for all symbol lengths. In another preferred embodiment, the length of the write gap recording field remains substantially greater than the minimum symbol length, but is less than the maximum symbol length. In such case, an additional extension pulse is applied having the same polarity as the immediately preceding pulse to form a magnetization vector having a symbol length greater than the length of the write gap recording field.
These and various other features and advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.